Special subframe configuration for latency reduction

ABSTRACT

The present disclosure relates to receiving and transmitting data in a frame with subframes of a wireless communication system, each subframe being either an uplink subframe accommodating uplink signal, a downlink subframe accommodating downlink signal or a special subframe including a downlink signal portion as well as an uplink signal portion. A control signal includes a special subframe configuration specifying the length of the uplink and/or downlink portion of the special subframe. The mapping and demapping of user data and/or control data including feedback information in a transmission time interval, TTI, onto or from one subframe is then performed, wherein the length of a second TTI for mapping onto the uplink portion of a special subframe is shorter than a first TTI for mapping onto an uplink subframe, or a first number of TTIs mapped onto the uplink subframe is larger than a second number of TTIs for mapping onto the uplink portion of a special subframe. The data are received or transmitted accordingly.

BACKGROUND Technical Field

The present disclosure relates to configuring subframes including bothuplink and downlink portions in a wireless communication system and totransmitting and receiving data in such subframes.

Description of the Related Art

Long Term Evolution (LTE)

Third-generation mobile systems (3G) based on WCDMA radio-accesstechnology are being deployed on a broad scale all around the world. Afirst step in enhancing or evolving this technology entails introducingHigh-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, alsoreferred to as High Speed Uplink Packet Access (HSUPA), giving a radioaccess technology that is highly competitive.

In order to be prepared for further increasing user demands and to becompetitive against new radio access technologies, 3GPP introduced a newmobile communication system called Long Term Evolution (LTE). LTE isdesigned to meet the carrier needs for high speed data and mediatransport as well as high capacity voice support for the next decade.The ability to provide high bit rates is a key measure for LTE.

The work item (WI) specification on Long-Term Evolution (LTE) calledEvolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial RadioAccess Network (UTRAN) is finalized as Release 8 (LTE Rel. 8). The LTEsystem represents efficient packet-based radio access and radio accessnetworks that provide full IP-based functionalities with low latency andlow cost. In LTE, scalable multiple transmission bandwidths arespecified such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order toachieve flexible system deployment using a given spectrum. In thedownlink, Orthogonal Frequency Division Multiplexing (OFDM) based radioaccess was adopted because of its inherent immunity to multipathinterference (MPI) due to a low symbol rate, the use of a cyclic prefix(CP) and its affinity to different transmission bandwidth arrangements.Single-carrier frequency division multiple access (SC-FDMA) based radioaccess was adopted in the uplink, since the provisioning of wide areacoverage was prioritized over improvement in the peak data rateconsidering the restricted transmit power of the user equipment (UE).Many key packet radio access techniques are employed includingmultiple-input multiple-output (MIMO) channel transmission techniquesand a highly efficient control signaling structure is achieved in LTERel. 8/9.

LTE Architecture

The overall architecture is shown in FIG. 1 and a more detailedrepresentation of the E-UTRAN architecture is given in FIG. 2. TheE-UTRAN consists of an eNodeB, providing the E-UTRA user plane(PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towardsthe user equipment (UE). The eNodeB (eNB) hosts the Physical (PHY),Medium Access Control (MAC), Radio Link Control (RLC) and Packet DataControl Protocol (PDCP) layers that include the functionality ofuser-plane header-compression and encryption. It also offers RadioResource Control (RRC) functionality corresponding to the control plane.It performs many functions including radio resource management,admission control, scheduling, enforcement of negotiated uplink Qualityof Service (QoS), cell information broadcast, ciphering/deciphering ofuser and control plane data, and compression/decompression ofdownlink/uplink user plane packet headers. The eNodeBs areinterconnected with each other by means of the X2 interface.

The eNodeBs are also connected by means of the S1 interface to the EPC(Evolved Packet Core), more specifically to the MME (Mobility ManagementEntity) by means of the S1-MME and to the Serving Gateway (SGW) by meansof the S1-U. The S1 interface supports a many-to-many relationshipbetween MMEs/Serving Gateways and eNodeBs. The SGW routes and forwardsuser data packets, while also acting as the mobility anchor for the userplane during inter-eNodeB handovers and as the anchor for mobilitybetween LTE and other 3GPP technologies (terminating S4 interface andrelaying the traffic between 2G/3G systems and PDN GW). For idle stateuser equipments, the SGW terminates the downlink data path and triggerspaging when downlink data arrives for the user equipment. It manages andstores user equipment contexts, e.g., parameters of the IP bearerservice, network internal routing information. It also performsreplication of the user traffic in case of lawful interception.

The MME is the key control-node for the LTE access-network. It isresponsible for idle mode user equipment tracking and paging procedureincluding retransmissions. It is involved in the beareractivation/deactivation process and is also responsible for choosing theSGW for a user equipment at the initial attach and at the time ofintra-LTE handover involving Core Network (CN) node relocation. It isresponsible for authenticating the user (by interacting with the HSS).The Non-Access Stratum (NAS) signaling terminates at the MME and it isalso responsible for generation and allocation of temporary identitiesto user equipment. It checks the authorization of the user equipment tocamp on the service provider's Public Land Mobile Network (PLMN) andenforces user equipment roaming restrictions. The MME is the terminationpoint in the network for ciphering/integrity protection for NASsignaling and handles the security key management. Lawful interceptionof signaling is also supported by the MME. The MME also provides thecontrol plane function for mobility between LTE and 2G/3G accessnetworks with the S3 interface terminating at the MME from the SGSN. TheMME also terminates the S6a interface towards the home HSS for roaminguser equipments.

Component Carrier Structure in LTE (Release 8)

The downlink component carrier of a 3GPP LTE (Release 8 and further) issubdivided in the time-frequency domain in so-called subframes. In 3GPPLTE (Release 8 and further) each subframe is divided into two downlinkslots, one of which is shown in FIG. 3. The first downlink slotcomprises the control channel region (PDCCH region) within the firstOFDM symbols. Each subframe consists of a given number of OFDM symbolsin the time domain (12 or 14 OFDM symbols in 3GPP LTE, Release 8 andfurther), wherein each OFDM symbol spans over the entire bandwidth ofthe component carrier. The OFDM symbols thus each consists of a numberof modulation symbols transmitted on respective N_(RB) ^(DL)×N_(sc)^(RB) subcarriers. Assuming a multi-carrier communication system, e.g.,employing OFDM, as for example used in 3GPP Long Term Evolution (LTE),the smallest unit of resources that can be assigned by the scheduler isone “resource block”. A physical resource block (PRB) is defined asN_(symb) ^(DL) consecutive OFDM symbols in the time domain (e.g., 7 OFDMsymbols) and N_(cs) ^(RB) consecutive subcarriers in the frequencydomain as exemplified in FIG. 3 (e.g., 12 subcarriers for a componentcarrier). In 3GPP LTE (Release 8), a physical resource block thusconsists of N_(symb) ^(DL)×N_(sc) ^(RB) resource elements, correspondingto one slot in the time domain and 180 kHz in the frequency domain (forfurther details on the downlink resource grid, see for example 3GPP TS36.211, v8.9.0, “Evolved Universal Terrestrial Radio Access (E-UTRA);Physical Channels and Modulation (Release 8)”, section 6.2, available athttp://www.3gpp.org and incorporated herein by reference).

One subframe consists of two slots, so that there are 14 OFDM symbols ina subframe when a so-called “normal” CP (cyclic prefix) is used, and 12OFDM symbols in a subframe when a so-called “extended” CP is used. Forthe sake of terminology, in the following the time-frequency resourcesequivalent to the same N_(sc) ^(RB) consecutive subcarriers spanning afull subframe is called a “resource block pair”, or equivalent “RB pair”or “PRB pair”.

The term “component carrier” refers to a combination of several resourceblocks in the frequency domain. In future releases of the LTE, the term“component carrier” is no longer used, instead, the terminology ischanged to “cell”, which refers to a combination of downlink andoptionally uplink resources. The linking between the carrier frequencyof the downlink resources and the carrier frequency of the uplinkresources is indicated in the system information transmitted on thedownlink resources.

Similar assumptions for the component carrier structure apply to laterreleases too.

Time Division Duplex—TDD

LTE can operate in Frequency-Division-Duplex (FDD) andTime-Division-Duplex (TDD) modes in a harmonized framework, designedalso to support the evolution of TD-SCDMA (Time-Division SynchronousCode Division Multiple Access). TDD separates the uplink and downlinktransmissions in the time domain, while the frequency may stay the same.

The term “duplex” refers to bidirectional communication between twodevices, distinct from unidirectional communication. In thebidirectional case, transmissions over the link in each direction maytake place at the same time (“full duplex”) or at mutually exclusivetimes (“half duplex”).

For TDD in the unpaired radio spectrum, the basic structure of RBs andREs is depicted in FIG. 4, but only a subset of the subframes of a radioframe are available for downlink transmissions; the remaining subframesare used for uplink transmissions or for special subframes. Specialsubframes are important to allow uplink transmission timings to beadvanced, so as to make sure that transmitted signals from the UEs(i.e., uplink) arrive roughly at the same time at the eNodeB. Since thesignal propagation delay is related to the distance between transmitterand receiver (neglecting reflection and other similar effects), thismeans that a signal transmitted by a UE near the eNodeB travels for ashort time than the signals transmitted by a UE far from the eNodeB. Inorder to arrive at the same time, the far UE has to transmit its signalearlier than the near UE, which is solved by the so-called “timingadvance” procedure in 3GPP systems. In TDD this has the additionalcircumstance of the transmission and reception occurring on the samecarrier frequency, i.e., downlink and uplink need to be duplexed in timedomain. While a UE far from the eNodeB needs to start uplinktransmission earlier than the near UE, conversely, a downlink signal isreceived by a near UE earlier than by the far UE. In order to be able toswitch the circuitry from DL reception to UL transmission, guard time isdefined in the special subframe. In order to manage the timing advanceproblem, the guard time for a far UE needs to be longer than for a nearUE.

FIG. 4 shows the frame structure type 2, particularly for a 5 msswitch-point periodicity, i.e., for TDD configurations 0, 1, 2 and 6. Inparticular, FIG. 4 illustrates a radio frame, being 10 ms in length, andthe corresponding two half-frames of 5 ms each. The radio frame consistsof 10 subframes each with 1 ms, where each of the subframes is assignedthe type of uplink (U), downlink (D) or special (S), as defined by oneof the Uplink-downlink configurations according to the table of FIG. 5.

This TDD structure is known as “Frame Structure Type 2” in 3GPP LTERelease 8 and later, of which seven different uplink-downlinkconfigurations are defined, which allow a variety of downlink-uplinkratios and switching periodicities. FIG. 5 illustrates the Table withthe 7 different TDD uplink-downlink configurations, indexed from 0-6,where “D” shall indicate a downlink subframe, “U” an uplink subframe and“S” a special subframe. These configurations differ from each other bythe number and location of the uplink (U) and downlink (D) subframes aswell as the special subframes for downlink-uplink switching in the TDDoperation (S). As can be seen therefrom, the seven available TDDuplink-downlink configurations can provide between 40% and 90% ofdownlink subframes (if, for simplicity, counting a special subframe as adownlink subframe, since part of such a subframe is available fordownlink transmission).

As can be appreciated from FIG. 5, subframe #1 (“#” meaning “number”) isalways a Special subframe, and subframe #6 is sometimes a specialsubframe, namely for TDD configurations 0, 1, 2 and 6. On the otherhand, for TDD configurations 3, 4 and 5, subframe #6 is destined fordownlink. The remaining subframes are uplink or downlink subframes.

Special subframes include three fields: DwPTS (Downlink Pilot TimeSlot), the GP (Guard Period) and UpPTS (Uplink Pilot Time Slot). Theyare used to separate uplink and downlink subframes. In the specialsubframes, uplink and downlink signals may be transmitted in therespective subframe fields UpPTS and DwPTS, respectively. They areseparated by a guard period also called the downlink-uplink switchingpoint. Uplink and downlink capacity in this irregular subframe S isreduced in comparison to a normal subframe implying that less bits offorward error correction redundancy can be employed for a giventransport block size or the transport block size itself is to bereduced.

FIG. 6 shows table on the special subframe configurations and, inparticular, lists the lengths of DwPTS (Downlink Pilot Time Slot) and ofUpPTS (Uplink Pilot Time Slot) in number if downlink symbols Nd andnumber of uplink symbols Nu, as defined for 3GPP LTE Release 11. Eventhough 3GPP defines the DwPTS and UpPTS lengths as multiples of thesampling frequency (Ts), they nevertheless represent a number of OFDM orSC-FDMA symbols that are contained in DwPTS and UpPTS, respectively. Forexample, in the special subframe configuration #1, the DwPTS lengthassuming a normal cyclic prefix is defined as 6592 Ts. For normal cyclicprefix, the length of the first and seventh OFDM symbols are each 2208Ts, while other symbols are 2192 Ts long. Therefore a DwPTS length of6592 Ts is equivalent to Nd=3 OFDM symbols: (2208+2192+2192) Ts=6592 Ts.The GP (Guard Period) can be derived by subtracting the relevant DwPTSand UpPTS lengths from the length (in number of symbols, or in multiplesof Ts) of the special subframe (for instance 14). The special subframeconfiguration is independent from the Uplink-Downlink configurationshown in FIG. 5, so that all combinations of those two configurationsare possible.

The special subframe configuration in table of FIG. 6 can take values0-9, each of which is associated with a particular configuration ofnumber of uplink and downlink symbols. The number of uplink and downlinksymbols further depends on the length of an uplink and downlink cyclicalprefix applied. As can be seen from the Table, the length of the uplinkportion (UpPTS) of the special frame is rather low and can take only 1or two symbols. Thus, the UpPTS is merely used for transmitting uplinksignals such as reference signals or random access requests in the formof an access preamble.

The TDD configuration applied in the system has an impact on manyoperations performed at the mobile station and base station, such asradio resource management (RRM) measurements, channel state information(CSI) measurements, channel estimations, PDCCH detection and HARQtimings. In particular, the UE reads the system information to learnabout the TDD configuration in its current cell, i.e., which subframe tomonitor for measurement, for CSI measuring and reporting, for timedomain filtering to get channel estimation, for PDCCH detection, or forUL/DL ACK/NACK feedback.

Logical and Transport Channels

The MAC layer provides a data transfer service for the RLC layer throughlogical channels. Logical channels are either Control Logical Channelswhich carry control data such as RRC signaling, or Traffic LogicalChannels which carry user plane data. Broadcast Control Channel (BCCH),Paging Control Channel (PCCH), Common Control Channel (CCCH), MulticastControl Channel (MCCH) and Dedicated Control Channel (DCCH) are ControlLogical Channels. Dedicated Traffic Channel (DTCH) and Multicast TrafficChannel (MTCH) are Traffic Logical Channels.

Data from the MAC layer is exchanged with the physical layer throughTransport Channels. Data is multiplexed into transport channelsdepending on how it is transmitted over the air. Transport channels areclassified as downlink or uplink as follows; Broadcast Channel (BCH),Downlink Shared Channel (DL-SCH), Paging Channel (PCH) and MulticastChannel (MCH) are downlink transport channels, whereas the Uplink SharedChannel (UL-SCH) and the Random Access Channel (RACH) are uplinktransport channels.

A multiplexing is then performed between logical channels and transportchannels in the downlink and uplink respectively.

Layer 1/Layer 2 (L1/L2) Control Signaling

In order to inform the scheduled users about their allocation status,transport format and other data-related information (e.g., HARQinformation, transmit power control (TPC) commands), L1/L2 controlsignaling is transmitted on the downlink along with the data. L1/L2control signaling is multiplexed with the downlink data in a subframe,assuming that the user allocation can change from subframe to subframe.User allocation might also be performed on a TTI (Transmission TimeInterval) basis, where the TTI length can be a multiple of thesubframes. The TTI length may be fixed in a service area for all users,may be different for different users, or may even by dynamic for eachuser. Generally, the L1/2 control signaling needs only to be transmittedonce per TTI. In LTE Release 8, the TTI is 1 ms, equivalent to onesubframe.

The TTI is a parameter in UMTS and LTE (and other digitaltelecommunication networks) related to encapsulation of data from higherlayers for transmission on the radio link layer. It TTI is also relatedto the size of the data blocks passed from the higher network layers tothe radio link layer. In particular, TTI determines the timing andgranularity of the mapping of data onto the physical layer. One TTI isthe time interval in which given data is mapped to the physical layer.

The L1/L2 control signaling is transmitted on the Physical DownlinkControl Channel (PDCCH). A PDCCH carries a message as a Downlink ControlInformation (DCI), which in most cases includes resource assignments andother control information for a mobile terminal or groups of UEs. Ingeneral, several PDCCHs can be transmitted in one subframe. In 3GPP LTE,assignments for uplink data transmissions, also referred to as uplinkscheduling grants or uplink resource assignments, are also transmittedon the PDCCH.

Generally, the information sent on the L1/L2 control signaling forassigning uplink or downlink radio resources (particularly LTE(-A)Release 10) can be categorized to the following items:

-   -   User identity, indicating the user that is allocated. This is        typically included in the checksum by masking the CRC with the        user identity;    -   Resource allocation information, indicating the resources        (Resource Blocks, RBs) on which a user is allocated. Note, that        the number of RBs on which a user is allocated can be dynamic;    -   Carrier indicator, which is used if a control channel        transmitted on a first carrier assigns resources that concern a        second carrier, i.e., resources on a second carrier or resources        related to a second carrier;    -   Modulation and coding scheme that determines the employed        modulation scheme and coding rate;    -   HARQ information, such as a new data indicator (NDI) and/or a        redundancy version (RV) that is particularly useful in        retransmissions of data packets or parts thereof;    -   Power control commands to adjust the transmit power of the        assigned uplink data or control information transmission;    -   Reference signal information such as the applied cyclic shift        and/or orthogonal cover code index, which are to be employed for        transmission or reception of reference signals related to the        assignment;    -   Uplink or downlink assignment index that is used to identify an        order of assignments, which is particularly useful in TDD        systems;    -   Hopping information, e.g., an indication of whether and how to        apply resource hopping in order to increase the frequency        diversity;    -   CSI request, which is used to trigger the transmission of        channel state information in an assigned resource; and    -   Multi-cluster information, which is a flag used to indicate and        control whether the transmission occurs in a single cluster        (contiguous set of RBs) or in multiple clusters (at least two        non-contiguous sets of contiguous RBs). Multi-cluster allocation        has been introduced by 3GPP LTE-(A) Release 10.

It is to be noted that the above listing is non-exhaustive depending onthe DCI format that is used, not all mentioned information items need tobe present in each PDCCH transmission.

Downlink control information occurs in several formats that differ inoverall size and also in the information contained in its fields. Thedifferent DCI formats that are currently defined for LTE are as followsand described in detail in 3GPP TS 36.212, v12.7.0, “Multiplexing andchannel coding”, Section 5.3.3.1 (available at http://www.3gpp.org andincorporated herein by reference). For further information regarding theDCI formats and the particular information that is transmitted in theDCI, please refer to the technical standard or to the book “LTE—The UMTSLong Term Evolution—From Theory to Practice”, Edited by Stefanie Sesia,Issam Toufik, Matthew Baker, Wiley, 2011, Chapter 9.3, incorporatedherein by reference.

In order that the UE can identify whether it has received a PDCCHtransmission correctly, error detection is provided by means of a 16-bitCRC appended to each PDCCH (i.e., DCI). Furthermore, it is necessarythat the UE can identify which PDCCH(s) are intended for it. This couldin theory be achieved by adding an identifier to the PDCCH payload;however, it is more efficient to scramble the CRC with the “UEidentity”, which saves the additional overhead. The CRC parity bits maybe calculated by using the entire payload. The parity bits are computedand attached. In the case where the UE transmit antenna selection is notconfigured or applicable, after attachment, the CRC parity bits arescrambled with the corresponding RNTI.

The scrambling may further depend on the UE transmit antenna selection.In the case where the UE transmit antenna selection is configured andapplicable, after attachment, the CRC parity bits are scrambled with anantenna selection mask and the corresponding RNTI. In both cases theRNTI is involved in the scrambling operation.

Correspondingly, the UE descrambles the CRC by applying the “UEidentity” and, if no CRC error is detected, the UE determines that thePDCCH carries its control information intended for itself. Theterminology of “masking” and “de-masking” is used as well, for theabove-described process of scrambling a CRC with an identity.

The “UE identity” mentioned above with which the CRC of the DCI may bescrambled can also be a SI-RNTI (System Information Radio NetworkTemporary Identifier), which is not a “UE identity” as such, but ratheran identifier associated with the type of information that is indicatedand transmitted, in this case the system information. The SI-RNTI isusually fixed in the specification and thus known a priori to all UEs.

In general, uplink control data in the LTE is transmitted eithertogether with user data on the Physical Uplink Shared Channel (PUSCH) oron the Physical Uplink Control Channel (PUCCH) within so called UplinkControl Information (UCI). The UCI comprises at least one of:

-   -   Scheduling requests    -   HARQ ACK/NACK in response to downlink data packets on the PDSCH    -   Channel State Information (CSI) including Channel Quality        Indicator (CQI) and/or Rank Indicator (RI) related to MIMO        transmission and/or Precoding Matrix Indicator (PMI).

For further information regarding the UCI formats and the particularinformation that is transmitted in the UCI, please refer to thetechnical standard or to LTE—The UMTS Long Term Evolution—From Theory toPractice, Edited by Stefanie Sesia, Issam Toufik, Matthew Baker, Wiley,2011, Chapter 16.3, incorporated herein by reference.

Physical Downlink Control Channel (PDCCH) and Physical Downlink SharedChannel (PDSCH)

The physical downlink control channel (PDCCH) carries for examplescheduling grants for allocating resources for downlink or uplink datatransmission. Multiple PDCCHs can be transmitted in a subframe.

The PDCCH for the user equipments is transmitted on the first N_(symb)^(PDCCH) OFDM symbols (usually either 1, 2 or 3 OFDM symbols asindicated by the PCFICH, in exceptional cases either 2, 3, or 4 OFDMsymbols as indicated by the PCFICH) within a subframe, extending overthe entire system bandwidth; the system bandwidth is typicallyequivalent to the span of a cell or component carrier. The regionoccupied by the first N_(symb) ^(PDCCH) OFDM symbols in the time domainand the N_(RB) ^(DL)×B_(sc) ^(RB) subcarriers in the frequency domain isalso referred to as a PDCCH region or control channel region. Theremaining N_(symb) ^(PDSCH)=2·N_(symb) ^(DL)−N_(symb) ^(PDCCH) OFDMsymbols in the time domain on the N_(RB) ^(DL)×B_(sc) ^(RB) subcarriersin the frequency domain is referred to as the PDSCH region or sharedchannel region (see below).

For a downlink grant (i.e., resource assignment) on the physicaldownlink shared channel (PDSCH), the PDCCH assigns a PDSCH resource for(user) data within the same subframe. The PDCCH control channel regionwithin a subframe consists of a set of CCE where the total number ofCCEs in the control region of subframe is distributed throughout timeand frequency control resource. Multiple CCEs can be combined toeffectively reduce the coding rate of the control channel. CCEs arecombined in a predetermined manner using a tree structure to achievedifferent coding rate.

On a transport channel level, the information transmitted via the PDCCHis also referred to as L1/L2 control signaling (for details on L1/L2control signaling see above).

There is a particular predefined timing relation between uplink resourceassignments received in a subframe and the corresponding uplinktransmission in PUSCH. Details are given in TS 36.213 v12.8.0 “3rdGeneration Partnership Project; Technical Specification Group RadioAccess Network; Evolved Universal Terrestrial Radio Access (E-UTRA);Physical layer procedures (Release 11)” Chapter 8.0 “UE procedure fortransmitting the physical uplink shared channel” incorporated herewithby reference. In particular, Table 8-2 of TS 36.213 defines theparameter k for the TDD configurations 0-6, where k indicates thepositive offset of the target of an uplink resource allocation receivedin a subframe; for TDD configuration 0 there is an additional definitionof the timing for uplink subframes 3 and 8, omitted herewith forsimplicity. For instance, the parameter k is 6 for subframe 1 of TDDconfiguration 1, meaning that an uplink resource allocation received insubframe 1 of TDD configuration 1 is intended for subframe 1+6=7 of TDDconfiguration 1, which indeed is an uplink subframe, etc.

Hybrid ARQ Schemes

A common technique for error detection and correction in packettransmission systems over unreliable channels is called hybrid AutomaticRepeat request (HARQ). Hybrid ARQ is a combination of Forward ErrorCorrection (FEC) and ARQ.

If a FEC encoded packet is transmitted and the receiver fails to decodethe packet correctly (errors are usually checked by a CRC (CyclicRedundancy Check)), the receiver requests a retransmission of thepacket. Generally (and throughout this document) the transmission ofadditional information is called “retransmission (of a packet)”,although this retransmission does not necessarily mean a transmission ofthe same encoded information but could also mean the transmission of anyinformation belonging to the packet (e.g., additional redundancyinformation).

Depending on the information (generally code-bits/symbols) of which thetransmission is composed, and depending on how the receiver processesthe information, the following Hybrid ARQ schemes are defined:

In Type I HARQ schemes, the information of the encoded packet isdiscarded and a retransmission is requested, if the receiver fails todecode a packet correctly. This implies that all transmissions aredecoded separately. Generally, retransmissions contain identicalinformation (code-bits/symbols) to the initial transmission.

In Type II HARQ schemes, a retransmission is requested, if the receiverfails to decode a packet correctly, where the receiver stores theinformation of the (erroneously received) encoded packet as softinformation (soft-bits/symbols). This implies that a soft-buffer isrequired at the receiver. Retransmissions can be composed out ofidentical, partly identical or non-identical information(code-bits/symbols) according to the same packet as earliertransmissions. When receiving a retransmission the receiver combines thestored information from the soft-buffer and the currently receivedinformation and tries to decode the packet based on the combinedinformation. (The receiver can also try to decode the transmissionindividually, however generally performance increases when combiningtransmissions.) The combining of transmissions refers to so-calledsoft-combining, where multiple received code-bits/symbols arelikelihood-combined and solely received code-bits/symbols are codecombined. Common methods for soft-combining are Maximum Ratio Combining(MRC) of received modulation symbols and log-likelihood-ratio (LLR)combining (LLR combing only works for code-bits).

Type II schemes are more sophisticated than Type I schemes, since theprobability for correct reception of a packet increases with everyreceived retransmission. This increase comes at the cost of a requiredhybrid ARQ soft-buffer at the receiver. This scheme can be used toperform dynamic link adaptation by controlling the amount of informationto be retransmitted. E.g., if the receiver detects that decoding hasbeen “almost” successful, it can request only a small piece ofinformation for the next retransmission (smaller number ofcode-bits/symbols than in previous transmission) to be transmitted. Inthis case it might happen that it is even theoretically not possible todecode the packet correctly by only considering this retransmission byitself (non-self-decodable retransmissions).

Type III HARQ schemes may be considered a subset of Type II schemes: Inaddition to the requirements of a Type II scheme each transmission in aType III scheme must be self-decodable.

Synchronous HARQ means that the re-transmissions of HARQ blocks occur atpre-defined periodic intervals. Hence, no explicit signaling is requiredto indicate to the receiver the retransmission schedule.

Asynchronous HARQ offers the flexibility of scheduling re-transmissionsbased on air interface conditions. In this case some identification ofthe HARQ process needs to be signaled in order to allow for a correctcombining and protocol operation. In 3GPP LTE systems, HARQ operationswith eight processes are used. The HARQ protocol operation for downlinkdata transmission will be similar or even identical to HSDPA.

In uplink HARQ protocol operation there are two different options on howto schedule a retransmission. Retransmissions are either “scheduled” bya NACK (also referred to as a synchronous non-adaptive retransmission)or are explicitly scheduled by the network by transmitting a PDCCH (alsoreferred to as synchronous adaptive retransmissions). In case of asynchronous non-adaptive retransmission the retransmission will use thesame parameters as the previous uplink transmission, i.e., theretransmission will be signaled on the same physical channel resources,respectively uses the same modulation scheme/transport format.

Since synchronous adaptive retransmissions are explicitly scheduled viaPDCCH, the eNodeB has the possibility to change certain parameters forthe retransmission. A retransmission could be for example scheduled on adifferent frequency resource in order to avoid fragmentation in theuplink, or eNodeB could change the modulation scheme or alternativelyindicate to the user equipment what redundancy version to use for theretransmission. It should be noted that the HARQ feedback (ACK/NACK) andPDCCH signaling occurs at the same timing. Therefore the user equipmentonly needs to check once whether a synchronous non-adaptiveretransmission is triggered (i.e., only a NACK is received) or whethereNode B requests a synchronous adaptive retransmission (i.e., PDCCH issignaled).

HARQ and Control Signaling for TDD Operation

As explained above, transmission of downlink or uplink data with HARQrequires that an ACKnowledgement ACK or Negative ACK be sent in theopposite direction to inform the transmitting side of the success orfailure of the packet reception.

In case of FDD operation, acknowledgement indicators related to datatransmission in a subframe n are transmitted in the opposite directionduring subframe n+4, such that a one-to-one synchronous mapping existsbetween the instant at which the transport is transmitted and itscorresponding acknowledgment. However, in the case of TDD operation,subframes are designated on a cell-specific basis as uplink or downlinkor special (see next chapter), thereby constraining the times at whichresource grants, data transmissions, acknowledgments and retransmissionscan be sent in their respective directions. The LTE design for TDDtherefore supports grouped ACK/NACK transmissions to carry multipleacknowledgements within one subframe.

For uplink HARQ, the sending (in one downlink subframe) of multipleacknowledgements on the Physical Hybrid ARQ Indicator CHannel (PHICH) isnot problematic since, when viewed from the eNodeB, this is notsignificantly different from the case in which single acknowledgementsare sent simultaneously to multiple UEs. However, for downlink HARQ, ifthe asymmetry is downlink-biased, the uplink control signaling (PUCCH)formats of FDD are insufficient to carry the additional ACK/NACKinformation. Each of the TDD subframe configurations in LTE (see below,and FIG. 5) has its own such mapping predefined between downlink anduplink subframes for HARQ purposes, with the mapping being designed toachieve a balance between minimization of acknowledgment delay and aneven distribution of ACK/NACKs across the available uplink subframes.Further details are provided in TS 36.213 v12.8.0 “3rd GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layerprocedures (Release 11)” Chapter 7.3 incorporated herewith by reference.

TS 36.213 v12.8.0 “3rd Generation Partnership Project; TechnicalSpecification Group Radio Access Network; Evolved Universal TerrestrialRadio Access (E-UTRA); Physical layer procedures (Release 11)” Chapter10.1.3, incorporated herein by reference explains the TDD HARQ-ACKfeedback procedure. Table 10.1.3-1 of TS 36.213 gives the downlinkassociation set index for the ACK/NACK/DTX responses for the subframesof a radio frame, wherein the number in the boxes for the TDDconfigurations indicates the negative offset of the subframe which HARQfeedback is transported in said subframe. For instance, subframe 9 forTDD configuration 0 transports the HARQ feedback of subframe 9−4=5;subframe 5 of TDD configuration 0 being indeed a downlink subframe (seeFIG. 5).

In a HARQ operation, the eNB can transmit a different coded version fromthe original TB in retransmissions so that the UE can employ incrementalredundancy (IR) combining to get additional coding gain over thecombining gain. However, in realistic systems, it is possible that theeNB transmits a TB to one specific UE on one resource segment, but theUE cannot detect the data transmission due to DL control informationlost. In this case, IR combining will lead to very poor performance fordecoding the retransmissions because the systematic data has not beenavailable at the UE. In order to mitigate this problem the UE shouldfeedback a third state, namely discontinuous transmission (DTX)feedback, to indicate that no TB is detected on the associated resourcesegment (which is different from NACK indicating the decoding failure).

As can be seen in FIG. 5, some uplink/downlink configurations are highlyasymmetrical. For instance, configuration 5 includes only a singleuplink subframe and 8 downlink subframes. Such configurations aresometimes denoted as heavy downlink. They may result in a relativelyhigh latency which is caused by limited resources for transmittingACK/NACK feedback on the uplink, corresponding to the transmitteddownlink data. The latency is due to less opportunities for the uplinkdata. In such cases, more than one ACK/NACK feedback responses arebundled by applying logical AND. Consequently, ACK is only sent if allacknowledgements in a bundle are positive, otherwise, the entire bundleis retransmitted. This may result generally in more retransmission andthus, increased latency.

BRIEF SUMMARY

One non-limiting and exemplary embodiment provides apparatuses andmethods for an efficient transmission and reception of data in specialsubframes which include both a downlink part and an uplink part.

According to an embodiment, an apparatus is provided for transmittingdata in a frame with subframes of a wireless communication system, eachsubframe being either an uplink subframe accommodating uplink signal, adownlink subframe accommodating downlink signal or a special subframeincluding a downlink signal portion as well as an uplink signal portion,the apparatus comprising: a receiver for receiving a control signalincluding a special subframe configuration specifying the length of theuplink and/or downlink portion of the special subframe; a mapper formapping user data and/or control data including feedback information ina transmission time interval, TTI, onto one subframe, wherein i) thelength of a second TTI for mapping onto the uplink portion of a specialsubframe is shorter than a first TTI for mapping onto an uplinksubframe, or ii) a first number of TTIs mapped onto the uplink subframeis larger than a second number of TTIs for mapping onto the uplinkportion of a special subframe; and a transmitter for transmitting themapped data.

According to an embodiment an apparatus is provided for receiving datain a frame with subframes of a wireless communication system, eachsubframe being either an uplink subframe accommodating uplink signal, adownlink subframe accommodating downlink signal or a special subframeincluding a downlink signal portion as well as an uplink signal portion,the apparatus comprising: a transmitter for transmitting a controlsignal including a special subframe configuration specifying the lengthof the uplink and/or downlink portion of the special subframe; areceiver for receiving data mapped on special subframes according to thespecial subframe configuration; and a mapper for demapping user dataand/or control data including feedback information in a transmissiontime interval, TTI, from one subframe, wherein i) the length of a secondTTI for mapping onto the uplink portion of a special subframe is shorterthan a first TTI for mapping onto an uplink subframe, or ii) a firstnumber of TTIs mapped onto the uplink subframe is larger than a secondnumber of TTIs for mapping onto the uplink portion of a specialsubframe.

According to an embodiment a method is provided for transmitting data ina frame with subframes of a wireless communication system, each subframebeing either an uplink subframe accommodating uplink signal, a downlinksubframe accommodating downlink signal or a special subframe including adownlink signal portion as well as an uplink signal portion, the methodcomprising: receiving a control signal including a special subframeconfiguration specifying the length of the uplink and/or downlinkportion of the special subframe; mapping user data and/or control dataincluding feedback information in a transmission time interval, TTI,onto one subframe, wherein i) the length of a second TTI for mappingonto the uplink portion of a special subframe is shorter than a firstTTI for mapping onto an uplink subframe, or ii) a first number of TTIsmapped onto the uplink subframe is larger than a second number of TTIsfor mapping onto the uplink portion of a special subframe; andtransmitting the mapped data.

According to an embodiment a method is provided for receiving data in aframe with subframes of a wireless communication system, each subframebeing either an uplink subframe accommodating uplink signal, a downlinksubframe accommodating downlink signal or a special subframe including adownlink signal portion as well as an uplink signal portion, the methodcomprising: transmitting a control signal including a special subframeconfiguration specifying the length of the uplink and/or downlinkportion of the special subframe; receiving data mapped on specialsubframes according to the special subframe configuration; and demappinguser data and/or control data including feedback information in atransmission time interval, TTI, from one subframe, wherein i) thelength of a second TTI for mapping onto the uplink portion of a specialsubframe is shorter than a first TTI for mapping onto an uplinksubframe, or ii) a first number of TTIs mapped onto the uplink subframeis larger than a second number of TTIs for mapping onto the uplinkportion of a special subframe.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The above and other objects and features of the present disclosure willbecome more apparent from the following description and preferredembodiments given in conjunction with the accompanying drawings inwhich:

FIG. 1 is a block diagram showing an exemplary architecture of a 3GPPLTE system,

FIG. 2 is a block diagram showing an exemplary overview of the overallE-UTRAN architecture of 3GPP LTE,

FIG. 3 is a schematic drawing showing an exemplary downlink resourcegrid of a downlink slot as defined for 3GPP LTE (as of Release 8/9),

FIG. 4 is a schematic drawing illustrating the structure of a radioframe, being composed of 10 subframes for a 5 ms switch-pointperiodicity,

FIG. 5 is a table showing the seven currently-standardized (static) TDDUL/DL configurations 0-6, the respective definitions of the 10 subframesand their switch-point periodicity,

FIG. 6 is a table illustrating possible special subframe configurations,

FIG. 7 is a block diagram illustrating the apparatuses for transmittingand receiving data using different configurations of special subframes,

FIGS. 8a-8c include an exemplary table of special subframeconfigurations,

FIG. 9 is a schematic drawing illustrating structure of a specialsubframe,

FIG. 10 is a schematic drawing illustrating two examples of mapping oftransmission time intervals onto special subframes,

FIG. 11 is a schematic drawing illustrating four examples of mapping oftransmission time intervals onto uplink and downlink subframes,

FIGS. 12a-12h include a table illustrating configurations of uplink anddownlink including additional special subframes, and

FIG. 13 is a flow diagram illustrating the receiving and transmittingmethods.

DETAILED DESCRIPTION

As shown in FIG. 6, the uplink portion (UpPTS) of a special subframe canonly have one or two symbols. In case of LTE, these symbols are SC-FDMAsymbols. The one or two symbols may be used for transmission of somereference signals (e.g., sounding reference signal, SRS) but are notenough to accommodate control data or user data. For instance, thisshort uplink portion is not sufficient to support PUSCH transmission(user data) or control data transmission including feedback informationsuch as positive and negative acknowledgements (ACK/NACK) or channelquality information. In other words, the data and control signalsprovided for mapping onto the physical layer within one uplink TTI maybe too long to be accommodated into the special subframe, even ifpuncturing is applied.

However, particularly in cases of high asymmetry between downlink anduplink capacity, it would be beneficial to use the additional capacityof the special subframes for transmitting of control or user data,particularly to improve the uplink capacity. For instance, as can beseen in FIG. 5, in the heavy downlink configuration such asconfiguration 5, the uplink subframe is only transmitted once per framewhich may result in a longer latency of the feedback for the paralleldownlink traffic. Moreover, there may insufficient resources fortransmitting feedback so that acknowledgement bundling or multiplexingis applied. However, application of bundling or multiplexing may lead toincreased losses of the feedback which on the other side alsocontributes to increasing the latency. This loss may occur for exampleif only one joint feedback bit needs to convey the ACK/NACK state fortwo transport blocks. Since it is more harmful to erroneously omit aNACK compared to an ACK, such a joint feedback bit would indicate NACKunless for both transport blocks an ACK is determined, in which case thejoint feedback would indicate ACK.

In order to maintain backward compatibility with an existing systemand/or to avoid interference issues, it is desirable to align thetransmission structure to the legacy TDD subframes. In particular, theuplink/downlink subframe assignment, the switching periodicity and thespecial subframe structure should be maintained.

According to the present disclosure, special subframes may be used forreducing the latency.

This may be achieved in conjunction with employing a short transmissiontime interval (sTTI), i.e., a TTI shorter then length of a subframe. Inparticular, in LTE typically TTI has a length of 1 ms corresponding tothe length of the subframe. Accordingly, a single TTI is typicallymapped onto a single subframe. With a short TTI, data may beindependently mapped to the respective uplink and downlink portions ofthe special subframes, too. A short TTI also reduces latency.

Better latency than previous generations of 3GPP Radio AccessTechnologies (RATs) was one performance metric that guided the design ofthe LTE. Packet data latency is important not only for the perceivedresponsiveness of the system; it is also a parameter that indirectlyinfluences the throughput. HTTP/TCP is the dominating application andtransport layer protocol suite used on the internet today. The typicalsize of HTTP-based transactions over the internet are in the range froma few 10's of Kbytes up to 1 Mbyte. In this size range, the TCP slowstart period is a significant part of the total transport period of thepacket stream. During TCP slow start the performance is latency limited.Hence, improved latency can improve the average throughput for thesetype of TCP-based data transactions. In addition, to achieve very highbit rates (in the range of Gbps with Rel-13 CA), UE L2 buffers need tobe dimensioned correspondingly. The longer the Round Trip Time is, thebigger the buffers need to be. The only way to reduce bufferingrequirements in the UE and eNB side is to reduce latency.

Radio resource efficiency could also be positively impacted by latencyreductions. Lower packet data latency could increase the number oftransmission attempts possible within a certain delay bound; hencehigher BLER targets could be used for the data transmissions, freeing upradio resources but still keeping the same level of robustness for usersin poor radio conditions. The increased number of possible transmissionswithin a certain delay bound could also translate into more robusttransmissions of real-time data streams (e.g., VoLTE), if keeping thesame BLER target. This would improve the VoLTE voice system capacity.

The latency can be reduced by TTI shortening and by reducing processingtimes. In particular, TTI lengths between 0.5 ms and one OFDM/SC-FDMAsymbol may be beneficial, taking into account impact on referencesignals and physical layer control signaling, as well as backwardscompatibility, i.e., allowing normal operation of UEs of the earlierreleases on the same carrier.

According to the present disclosure, a shorter TTI is used to map userdata or control data onto an uplink or downlink portion of the specialsubframe. The short TTI is shorter than the duration of the subframe. Inparticular, the short TTI may correspond (be equal) to the duration of adownlink or an uplink portion of the special subframe or be shorter thanthat.

In order to further provide a possibility of mapping data into uplinkportion (and/or downlink portion) of the special subframes, thestructure of the special subframes is modified with respect to thelegacy special subframes (cf FIG. 6).

FIG. 7 shows a communication between a base station (eNB) and a terminal(user equipment, UE). Accordingly, a terminal may include a device 700Bfor transmitting data in a frame with subframes of a wirelesscommunication system. The wireless communication system may be the LTEsystem, which may operate as a cellular network and/or in adevice-to-device mode. The frame may then correspond to the radio framewhich is currently defined to include 10 subframes as described abovewith reference to FIG. 4. Each such subframe is either an uplinksubframe accommodating uplink signal, a downlink subframe accommodatingdownlink signal or a special subframe including a downlink signalportion as well as an uplink signal portion.

In the uplink direction, the terminal (UE) transmits data to the basestation. In the downlink direction, the terminal receives data from thebase station. The data may be user data (i.e., data generated by a userapplication possibly including control overhead of the higher layers) orcontrol data such as layer 1/layer 2 signaling including feedbackinformation. The feedback information may comprise HARQ positive ornegative acknowledgements, channel quality indication, rank indicator orPMI.

It is noted that the same device may also be implemented in a relay nodecommunicating with the base station via backhaul link.

The device 700B comprises a receiver 720 and a transmitter 740. Thereceiver as well as transmitter may embody features necessary forreception and transmission of data such as antennas, amplifiers, or thelike, implemented for instance within a dedicated or programmablecircuitry (hardware).

The receiver 720 is configured for receiving a control signal includinga special subframe configuration specifying the length of the uplinkand/or downlink portion of the special subframe. The control signal maybe control signaling transmitted on any layer. For instance, the controlsignal may be received via cell broadcast within system informationblocks. The control signal may be provided semi-statically via dedicatedRRC protocol or via a L1/L2 control signal such as the DCI in LTE, wherethe control signal could be valid to a single UE, or to a group of UEsincluding all UEs in the cell.

Transmitting the control signal via a cell broadcast such as in a systeminformation block of LTE has the advantage that the information can beconveyed to multiple recipients with little relative overhead. This isparticularly advantageous for cells where all UEs are expected tooperate in the same way as far as the scope of this disclosure isconcerned. For example a small cell, i.e., a cell that has a smallcoverage area and/or few connected UEs, can operate beneficially in sucha manner. Conveying the control signal via a dedicated RRC message hasthe benefit of a possible acknowledgement by the receiver that thecontrol signal has been received and processed correctly. Therefore thisis advantageous if an unsynchronized behavior due to errors should beavoided, especially when the configuration conveyed by the controlsignal is not expected to change in a timescale of up to 320 subframes.Conveying the control signal via a L1/L2 control signal has the mainbenefit in the possibility to quickly adapt the configuration to ad hocneeds, such as a highly fluctuating traffic change due to the datatraffic model. Such a L1/L2 control signal may additionallyadvantageously be directed to a group of UEs, identified by a commonradio network temporary identifier (RNTI) that is applied, in a similarfashion as dynamic TDD reconfiguration messages are supported in LTE (cf3GPP TS 36.213, v12.8.0, Section 13.1). The utilization of a dedicatedRRC message and a L1/L2 control signal has a benefit in case of largecells, i.e., supporting a wide area or many connected UEs. In such acase, especially in TDD the UEs close to the cell center and the UEsclose to the cell edge face large propagation delays, so that theirtiming advance offset to compensate for the propagation delay will needto be different. Consequently, a UE close to the cell edge may need alonger GP than a UE close to the cell center, so that a UE close to thecell center would be generally allowed to have a longer DwPTS+UpPTS(uplink portion and/or downlink portion of the special subframe) lengththan a UE close to the cell edge.

The special subframe configuration is advantageously one of a set ofpredefined configurations. These configurations in the set may differ inlength of the uplink portion, downlink portion and/or the guard periodbetween them. For instance, in LTE, the special subframe has a length of14 symbols, and the subframe configuration indicates which of thesymbols are assigned for uplink portion, downlink portion and the GP. Itis noted that for some scenarios, configurations having GP with zerosymbols (i.e., no GP between the last symbol of the downlink portion andthe first symbol of the uplink portion) may also be considered.Particularly for the case that the GP is shorter than one symbol, a partor all of the cyclic prefix of the first symbol of the uplink portionmight be used to accommodate the timing advance offset, i.e., the UE maybe allowed to omit transmission of part of the samples constituting thatcyclic prefix.

The received special subframe configuration is then adopted by thedevice. For instance, a controller 735 configures the device 700Baccordingly.

The device 700B further includes the mapper 730 for mapping user dataand/or control data including feedback information in a transmissiontime interval, TTI, onto one subframe.

In particular, the mapper receives data within a TTI and maps thereceived data onto the uplink portion of the special subframe or onto anuplink subframe for transmission. The mapping may include for instancein case of LTE the SC-FDMA the symbol forming. The data is received bythe mapper from within the device 700B. For instance, user data may bereceived from the medium access control (MAC) layer. The control datamay be generated in or between the MAC (layer 2) and the physical layer(layer 1). For instance, the acknowledgements may be generated by theHARQ entity, whereas the channel state feedback may be generated inresponse to physical layer measurements of the channel.

The length of a second TTI (short TTI) for mapping onto the uplinkportion of a special subframe may be shorter than a first TTI (legacyTTI) for mapping onto an uplink subframe. Alternatively, a first numberof TTIs mapped onto the uplink subframe is larger than a second numberof TTIs for mapping onto the uplink portion of a special subframe. Here,the length of the TTI may be equal for the mapping onto special anduplink subframes. For instance, a preconfigured length of a TTI may beused which is shorter than a legacy TTI length, or in other words thelength of a single subframe. However, it is noted that in general, thedisclosure is not limited to the same TTI length. Merely, the lengthand/or the number of TTIs is to be selected for the portions of thespecial frames as well as for the uplink or downlink frames to matchtheir duration.

The device 700B further comprises a transmitter 740 for transmitting themapped data in the respective uplink subframe and the uplink portion ofa special subframe.

Correspondingly, apparatus 700A for receiving data in the frame withsubframes of the wireless communication system may be a part of a basestation.

The apparatus 700A includes a transmitter 710 for transmitting a controlsignal including a special subframe configuration specifying the lengthof the uplink and/or downlink portion of the special subframe.Accordingly, the base station, which has information concerning the cellresources and quality and also performs scheduling, is capable ofconfiguring the special subframe configuration to be used incommunication with the UEs.

Moreover, the apparatus 700A further comprises a receiver 750 forreceiving data mapped on special subframes according to the specialsubframe configuration. These are the uplink data transmitted by therespective UEs in the cell.

A mapper 760 then demapps the data (user data and/or control dataincluding feedback information) in a transmission time interval, TTI,from one subframe, wherein the length of a second TTI for mapping ontothe uplink portion of a special subframe is shorter than a first TTI formapping onto an uplink subframe, or a first number of TTIs mapped ontothe uplink subframe is larger than a second number of TTIs for mappingonto the uplink portion of a special subframe.

It is noted that the apparatus 700A may include a controller 765, whichcontrols the transmitter 710 to transmit an appropriate configurationsand which controls the mapper 760 accordingly to demap the datareceived.

The above description concentrated on the uplink configuration andtransmission. However, the present disclosure is not limited thereto. Inparticular, the receiver of the apparatus 700B (which may be a part of aUE) can also be configured to receive data in the downlink, includingthe downlink portion of the special subframe(s). For instance, based onthe special subframe configuration received from the base station, theapparatus 700B receives downlink data in the specified TTI or aplurality of TTIs within the downlink portion of the special subframe.The downlink data may include user data (PDSCH) and/or control data suchas L1/L2 control signals conveying scheduling information, for examplethe downlink control information (DCI) carried by PDCCH/EPDCCH in LTE.

As shown in FIG. 7, the transmitter 710 of the apparatus 700A mayprovide the receiver 720 of the apparatus 700B not only with theconfiguration of special frames and/or uplink/downlink frames (dashedline), but also with data mapped according to the configuration(dash-dotted line). On the other hand, the transmitter 740 of theapparatus 700B provides the receiver 750 of the apparatus 700A with theuplink data (user or control data).

Correspondingly, the apparatus 700A which may be implemented in a basestation has the transmitter, which may be additionally configured totransmit data to a UE or a plurality of UEs in the downlink portion ofthe special subframe(s) as configured by the special subframeconfiguration.

FIG. 8 (in its parts 8 a, 8 b, and 8 c) illustrates an example of anextended table of configurations for special subframes.

Accordingly, the special subframe configuration takes a value out of avalue set (0-65), wherein some configurations in the set differ withrespect to the length of the downlink portion, uplink portion and thelength of the TTI.

In particular, the first 9 configurations in FIG. 8 correspond toconfigurations described with reference to FIG. 6. Configurations 10 to65 enable accommodating of multiple short TTI's for downlink and/oruplink. In order to achieve this, the length of the downlink portionand/or uplink portion of the special subframe are modified to provide alarger number of choices. In some of the cases, the guard period betweenthe downlink portion and the uplink portion is shortened to provide morespace (symbols) for uplink and downlink short TTI. In particular thiscan be seen in FIG. 8, configurations with longer uplink portion of thespecial subframe are provided for both normal and extended cyclicprefix.

In the table, special configurations numbered from 0 to 65 are provided.Configurations 21 to 65 provide a longer uplink portion of the specialsubframe, namely uplink portion of the length between 3 and 11 SC-FDMAsymbols. Various lengths of the downlink portion are possible resultingin various lengths of the guard period (it is assumed that specialsubframe has 14 symbols and at least one symbol for guard period).

FIG. 8 is merely exemplary. A different number or order of possibleconfigurations may be provided. For instance, in order to limit numberof bits necessary for signaling, the number of special subframeconfigurations may be limited to 16 (4 bits), 32 (5 bits), 64 (6 bits)or 128 (7 bits). Moreover, there may be configurations resulting inguard period with length of less than one symbol or even zero. FIG. 8should not be understood as tying the special subframe configurationindex to a specific configuration; for example it is not importantwhether configuration number 19 represents 7 symbols in DwPTS and 2symbols in UpPTS, or 6 symbols in DwPTS and 3 symbols in UpPTS.Likewise, FIG. 8 should not be understood to mean that a certaincombination of symbols in DwPTS/UpPTS for a normal cyclic prefix impliesthat in case of an extended cyclic prefix the combination of symbolsneeds to be exactly as given in FIG. 8. For example, FIG. 8 listsconfiguration number 19 as supporting 7 symbols in DwPTS and 2 symbolsin UpPTS for the case of a normal cyclic prefix in both uplink anddownlink. However in contrast to FIG. 8, it is possible thatconfiguration number 19 supports 6 symbols in DwPTS and 2 symbols inUpPTS for the case of an extended cyclic prefix in both uplink anddownlink (i.e., the numerology shown for configuration number 18 forthat case).

The table shown in FIG. 8 provides the advantage of supporting the first10 configurations which are currently specified for LTE legacy system(up to release 13). The additional configurations are new and may besupported starting from release 14.

FIG. 8 shows many configurations for both normal cyclic prefix andextended cyclic prefix in the downlink as well as in uplink. However,the present disclosure is not limited thereto. The number ofconfigurations may be reduced. For instance, in order to support latencyreduction, it may be beneficial not to support extended cyclic prefix inuplink or in downlink or in both of them.

Cyclic prefix (CP) is a portion preceding each symbol in LTE (indownlink OFDM symbol, in uplink SC-FDMA symbol). In LTE, the length ofthe cyclic prefix is ca. 5 microseconds. The purpose of the cyclicprefix is to separate the symbols to be able to compensate for frequencyshifts occurring for instance due to high mobility. Apart from thenormal CP, LTE also defines an extended CP, which has a duration of ca.17 microseconds. This is to ensure that even in large suburban and ruralcells, the delay spread should be contained within the CP.

Since not all configurations are necessarily attractive for certainuplink and/or downlink TTI lengths and cell sizes, the number ofconfigurations may be further reduced, i.e., not all possibleconfigurations of uplink and downlink portion lengths are to be listedin the table and thus available for configuring. For example, a closeinspection of FIG. 8 shows that configurations number 55, 59, 62, 64, 65represent configurations that are only applicable if the cyclic prefixis “normal” in downlink as well as in uplink, and therefore have alimited potential applicability. Therefore if at least two of theseconfigurations are unavailable, at most 64 configurations are availablethat can be efficiently represented by 6 bits.

In addition or alternatively, special subframe configuration value(index in the first column of the table in FIG. 8) may be unique onlyfor certain TTI length. For instance, configuration #10 (with index 16)may indicate number of DwPTS symbols (OFDM symbols) 2 and UpPTS(SC-FDMA) symbols 2 for TTI length 0.2 ms in downlink and uplinkportion, but number of DwPTS symbols 5 and 5 for TTI length 0.5 ms. Assuch, the interpretation of the configuration may take the TTI length asa parameter, where the TTI length is configured by a configurationsignal that is not tied to the special subframe configuration.

Alternatively, the special subframe configuration may imply a TTI lengthat least for the uplink portion and/or the downlink portion. Forexample, special subframe configurations indicating a number n1 of DwPTSsymbols imply that the corresponding downlink TTI is at most n1 symbolslong. Likewise, special subframe configurations indicating a number n2of UpPTS symbols imply that the corresponding uplink TTI is at most n2symbols long.

In general, the special subframe configuration advantageously takes avalue (index, e.g., illustrated in the first column of Table in FIG. 8)out of a value set in which at least a first value indicates length ofthe uplink portion of the special subframe which is not sufficient toaccommodate the data in the second TTI, and a second value indicateslength sufficient to accommodate the data in the second TTI but not datain the first TTI.

In other words, special subframe configurations include at least onelegacy configurations including uplink portion length too short toaccommodate even a short TTI and at least one new configuration withuplink portion length sufficient to accommodate a short TTI (but notsufficient to accommodate the TTI for normal uplink subframes). This maybe the case for instance if the length of the short TTI is 12 of thelegacy TTI. In such case configurations 0 to 9 in FIG. 8 cannotaccommodate such short TTI since they provide uplink portion length ofonly up to 2 symbols. However, configurations 38 to 65 could accommodatesuch short TTI.

The mapper 730 is then advantageously configured to:

-   -   map onto the uplink portion physical layer signals including        sounding reference signals if the special subframe configuration        takes the first value; and    -   map onto the uplink portion control data including positive or        negative acknowledgements for downlink data and/or channel state        information if the special subframe configuration takes the        second value; or    -   map onto the uplink portion user data if the special subframe        configuration takes the second value.

In other words, if the uplink portion of a special subframeconfiguration is not sufficiently long enough to accommodate any (or theconfigured) TTI, such an uplink portion may be used for providing pilotsignals such as sounding reference signals. Alternatively or in additionsuch an uplink portion may be used to transmit some other physical layersignals such as preambles used for (initial) random access, i.e., forcollision avoidance. On the other hand, if the uplink portion of thespecial subframe configuration is sufficiently long to accommodate theTTI, the uplink portion may be used for the transmitting of user data orcontrol signals or both of them.

As already mentioned above, each special subframe may consist of aplurality of symbols and the special subframe configuration indicatesthe number of symbols for the downlink portion and/or for the uplinkportion, and the special subframe may further comprise a guard period ofone or more symbols separating the downlink portion and the uplinkportion.

However, it is noted that the special subframe configuration may ingeneral also be defined only by the length of the downlink portion oronly by the length of the uplink portion in case the guard period andthe length of the special subframe is fixed. Any alternatives arepossible as long as the special subframe configuration is capable ofindicating the assignment of particular symbols to a particular purpose(uplink, downlink, guard period).

FIG. 9 shows a detail structure of the special subframe alreadyillustrated in FIG. 4. In particular, a special subframe may start withNd downlink symbols (DwPTS), include a guard period (GP) separatingthese downlink symbols from the following Nu uplink symbols (UpPTS). Inthe TDD LTE, the special subframe has the length of 30720 sample periodsTs which is equal to 1 ms.

FIG. 10 illustrates some exemplary mappings of TTIs onto a specialsubframe. For instance, in the upper example the length of the TTIdiffers for the uplink part of a special subframe and a downlink part ofa special subframe. At the same time the number of TTIs differs for theuplink part of the special subframe and for the downlink part of thespecial subframe. In particular, in this example two short downlink TTIsare mapped onto the downlink portion of the special subframe. Moreover,three short uplink TTIs are mapped onto the uplink portion of thespecial subframe. The length of the uplink TTI is greater than thelength of the downlink TTI. At the same time the number of downlink TTIsis smaller than the number of uplink TTIs.

The bottom example of FIG. 10 shows another configuration, in which thenumber of downlink TTIs is greater than the number of uplink TTIs. Atthe same time, the length of the downlink TTI is smaller than the lengthof the uplink TTI. The guard period in this example is also shorter withrespect to the guard period of the upper example. A shorter guard periodmay be acceptable especially for small cells due to smaller timingadvance requirements.

The length of the TTI determines the amount of data which may beconveyed within the TTI. The number of TTIs determines the frequencywith which the data can be collected for mapping onto the resource grid.Together the length of the TTI and their number thus have an impact onthe latency. As already mentioned above, the present disclosure is notlimited to these examples. For instance, there may be a single TTImapped on the downlink portion of the special subframe and a single TTImapped on the uplink portion of the special subframe. Such uplink anddownlink TTI may be of the same length or of a different lengthdepending on the special subframe configuration, i.e., on the number ofsymbols per portion. Alternatively, a short TTI of the samepreconfigured length may be applied to both uplink and downlink, withthe number of such short TTIs being different for the uplink anddownlink portions.

In addition, shorter TTI is may also be applied to uplink subframes,downlink subframes or both of them as is shown in FIG. 11. Inparticular, FIG. 11 shows four examples (assuming a normal CP for uplinksymbols as well as for downlink symbols, without loss of generality) inwhich one 1 ms subframe accommodates 14, seven, four, or two TTIs.Example (a) illustrates subframe onto which data in 14 TTIs are mapped.Each TTI has a length of one symbol (OFDM symbol for downlink, SC-FDMAsymbol for uplink). Thus, a TTI correspond to the duration of onesymbol. The major advantage of a very short TTI such as one symbol isthe ability to process the data very quickly, e.g., the decodingprocedure can be started immediately after the reception of the symbol.In contrast, a 1 ms TTI implies that the whole subframe (=1 ms) needs tobe received before the decoding procedure can be started. Therefore incase of a short TTI, the data as well as the corresponding ACK/NACKfeedback are available much sooner at the receiver, and the ACK/NACK canbe conveyed back to the transmitted much earlier than for the 1 ms TTIcase.

Example (b) shows one subframe into which seven short TTIs are mapped,each having the duration of two symbols. Example (c) shows one subframeinto which for TTIs are mapped. This TTI is differ in their size. Inparticular, two TTIs with a length of three symbols and two TTIs with alength of 4 symbols can be seen, mapped alternately (TTI(3 symbols),TTI(4 symbols), TTI(3 symbols), TTI(4 symbols)). Finally, example (d)shows two TTIs per subframe, each of the two TTIs having the length ofseven symbols. While these TTI lengths lose some of the gains mentionedfor the one symbol TTI, there is the advantage that these TTIs cansupport larger transport blocks. Especially considering advanced forwarderror correction schemes such as turbo coding or low-density paritycheck coding, the coding gain increases with the length of the encodedtransport block. Another advantage is that usually the transmit power islimited per transmitted symbol, so that a TTI comprising multiplesymbols can convey more energy and therefore obtain a higher SINRcompared to a single symbol as far as the total energy per transportblock or TTI is concerned. This is particularly advantageous for uplinktransmissions where the transmit power is usually more limited that fordownlink due to the hardware cost for the power amplifiers employed inan eNB and a UE.

As described above, in LTE currently the uplink portion of the specialsubframes cannot be used for transmitting control or user data. Since itis very short (1-2 symbols), the uplink portion is only used to transmitsome uplink signals such as sound reference signals and/or preambles forthe random access (initial access). Random access is used by the UEs toobtain channel access. It is an unscheduled access in which collisionsmay occur. In order to enable distinguishing the UEs in the randomaccess, pseudo-random sequences with good cross-correlation propertiesand good auto-correlation properties are used. In particular, a UEselects randomly a sequence (preamble) and transmits it together withits identifier to the base station to obtain resources for transmission.

According to one example of the present disclosure, the uplink portionof the special subframe consists of a data portion onto which user dataand/or control data is mapped within one or more TTIs and a signalportion which carries sounding reference signal and/or a random accesschannel preamble. For instance, the uplink portion of the specialsubframe may accommodate one or more TTIs and, in addition, apredetermined number of symbols (e.g., 1 or 2) forming the signalportion for transmitting the reference signals and/or initial accesspreambles. Advantageously, the symbols of the signal portion are thelast symbols of the uplink portion. In particular, this configuration iscompliant with the configuration of the current LTE system. Compliancetherewith enables using the sounding reference signal by UEs ofdifferent standard versions and avoids interfering with the PUSCHtransmissions.

According to an embodiment, new special subframes are introduced withina radio frame apart from the legacy switching subframes 1 and 6 shown inFIG. 5. Such new special subframes may be available for UE starting fromrelease 13 of LTE, in which a shorter TTI is configurable.

Such new special subframes are advantageously configured in thosesubframes which are configurable as Multimedia Broadcast SingleFrequency Network (MBSFN) subframes in LTE.

One of the targets of MBSFN is supporting of multimedia (e.g., TV)multicast or broadcast over LTE.

In particular, according to TS 36.211, v12.8.0, “Physical channels andmodulation” clause 6.1 which is incorporated herewith by reference, asubset of the downlink subframes in a radio frame on a carriersupporting PDSCH transmission can be configured as MBSFN subframes byhigher layers. Each MBSFN subframe is divided into a non-MBSFN regionand an MBSFN region. The non-MBSFN region spans the first one or twoOFDM symbols in an MBSFN subframe where the length of the non-MBSFNregion is given by Table corresponding to Table 6.7-1 from the abovecited TS 36.211. Transmission in the non-MBSFN region shall use the samecyclic prefix length as used for subframe 0. The MBSFN region in anMBSFN subframe is defined as the OFDM symbols not used for the non-MBSFNregion.

TABLE 1 Number of OFDM Number of OFDM symbols for PDCCH symbols forPDCCH Subframe when N_(RB) ^(DL) > 10 when N_(RB) ^(DL) ≤ 10 Subframe 1and 6 for 1, 2 2 frame structure type 2 MBSFN subframes on a 1, 2 2carrier supporting PDSCH, configured with 1 or 2 cell- specific antennaports MBSFN subframes on a 2 2 carrier supporting PDSCH, configured with4 cell- specific antenna ports Subframes on a carrier not 0 0 supportingPDSCH Non-MBSFN subframes 1, 2, 3 2, 3 (except subframe 6 for framestructure type 2) configured with positioning reference signals Allother cases 1, 2, 3 2, 3, 4

In an MVBSFN subframe, cell-specific reference signals are onlytransmitted in the non-MBSFN region of the MBSFN subframe. Theconfiguration of the MBSFN subframes is performed via RRC protocol. Inparticular, the configuration is transmitted within system informationblock (SIB) number 2 from the eNodeB (base station) to the terminal(s).Within the RRC, the MBSFN configuration is embedded in Informationelement mbsfnu-SubframeConfigList, which also defines the subframes thatare reserved for MBSFN in downlink.

Configurability of the MBSFN subframes are special subframes providingthe advantage of reduced interference and backward compatibility. Inparticular, as mentioned above, MBSFN subframes transmit control andreference signals only in the first two OFDM symbols. Accordingly, theremaining portion of an MBSFN may be used for mapping uplink signalthere on without risk of misinterpreting the uplink signals by thelegacy UEs as reference or PDCCH signals. As has been also shown in FIG.8, in a special subframe having only two to three downlink OFDM symbolsreserved for downlink and small guard period (suitable for small cellswith small time advance), up to 11 SC-FDMA symbols might be usable foruplink. Such configuration is also possible with MBSFN subframes. Theyprovide the advantage of reducing latency especially for heavy downlinksince they may be used to convey HARQ feedback and/or PUSCH sTTIs, i.e.,uplink user data.

In other words, in this embodiment, the control signal further comprisesan uplink/downlink configuration specifying for each subframe of a framewhether it is downlink, uplink or special subframe, and theuplink/downlink configuration includes a first set of subframes that areconfigurable for multicast or broadcast, and a second set of subframesthat are not configurable for multicast or broadcast.

FIG. 12 (in its parts 12 a to 12 h) illustrates an example ofuplink/downlink configurations including such additional specialsubframes which are marked by “A” in the figure. In particular,configurations with index 0, 1, 2, 3, 4, 5, and 6 correspond to therespective configurations of the table in FIG. 5 and thus do not includeadditional special subframes. New configurations have been added basedon these seven legacy configurations by replacing one or more subframesconfigurable for MBSFN (i.e., subframes number 3, 4 and 7, 8, 9) withadditional special subframes.

Another advantage of using MBSFN subframes for those subframes is thatalready some HARQ timing relation between downlink and uplink isdefined. This is currently established in Table 10.1.3.1-1 of the TS36.213, v12.8.0 where for subframes 3, 4, 7, 8, 9 (i.e., those subframesthat are configurable for MBSFN) at least one UL/DL configuration isavailable that defines the HARQ timing relation between downlink dataand corresponding uplink ACK/NACK; therefore those established timingrelations could be re-used without great additional efforts. Moreover,subframe number six can be a beneficial candidate because it is aspecial subframe already in some configurations.

The additional special subframes (A) advantageously take into accountthe length of the (short) TTI configurable for uplink. This enablestransmission of control data and user data in the uplink part of thespecial subframes as already also discussed above. In particular, sPUCCHand sPUSCH transmissions are possible. With “sPUCCH” and “sPUSCH” therespective short versions of physical uplink control channel on physicaluplink shared channel are denoted. The short versions of the physicaluplink channels differ from the currently used PUCCH and PUSCH by thesupport of a short TTI (sTTI) or a plurality of possible configurablesTTIs.

Special subframe configurations advantageously differ for the first andthe second sets of subframes of the uplink/downlink configuration, i.e.,for the subframes 3, 4, 7, 8, 9 (A) configurable for MBSFN and for theremaining subframes 1, 6 (S). However, since subframe #6 may be used asboth a legacy downlink subframe or a special subframe, both or any ofspecial subframe configurations may be configurable for the subframe.

In other words, in order to facilitate coexistence with the legacy UEs,it may be advantageous to have two independent special subframeconfigurations or configurations sets applicable for the legacy specialsubframes (S) and the additional special subframes (A).

It is noted that FIG. 12 shows many different uplink/downlinkconfigurations. However, the present disclosure is not limited toproviding all these combinations as configurable. Rather, the set ofconfigurable uplink/downlink configurations may be limited to a subsetof the table shown in FIG. 12. Selection of the set size is a tradeoffbetween the configuration flexibility (provided by a large choice, i.e.,by all possible configurations included in the set) and between thememory and transmission capacity required to store and signal therespective selected configuration.

In summary, according to one embodiment, the wireless communicationsystem is a long term evolution (LTE), the first set of subframes arefrom among those subframes that are configurable as multicast broadcastsingle-frequency network, MBSFN, subframes, or the second set ofsubframes are subframes with number 1 and/or 6.

In the above described example, various configurations of specialsubframes have been shown and discussed. In wireless communicationsystems, there are typically several different channels mapped onto theavailable resources. These channels may carry different types of signals(control or user data) with different requirements concerningreliability and latency. Accordingly, it may be advantageous to employdifferent special subframe configurations for different channels. Inparticular, the shared channel (PDSCH) may employ a different TTI lengthor number of TTIs than the control channel (PUSCH). For instance, uplinkshared channel may occupy more symbols than the uplink control channel.This may be achieved by configuring, for the uplink shared channel(which may convey user data) a larger TTI and/or more TTIs within theuplink portion of the special subframe than for the uplink controlchannel.

It is noted that the above description exemplifies the presentdisclosure based on the LTE system. However, the present disclosure isnot limited thereto. Any wireless communication system employing specialsubframes which are used to accommodate both uplink parts and downlinkparts may embody the present disclosure.

Moreover, the above examples manly refer to a communication between abase station and the terminal. However, in general, the above approachmay also be used in communication between two nodes such as two userequipments (device to device communication). In such case, the terms“uplink” and “downlink” would merely refer to a first and a seconddirection of transmission (i.e., from UE1 to UE2 and from UE2 to UE1respectively).

Currently, the uplink/downlink configuration and special subframeconfiguration are transmitted from the base station to the UEs over RRCprotocol within the system information. However, it may be beneficial toenable reconfiguration of the sTTI length and/or short-TTI specialsubframe positions and lengths dynamically.

According to an embodiment, thus the control signal carrying the specialsubframe configuration is transmitted within downlink controlinformation as layer 1/layer 2 signaling.

Such dynamic configuration may be performed in a similar manner as inthe enhanced Interference Mitigation and Traffic Adaption (eIMTA), whichis a mechanism for reconfiguring TDD uplink/downlink configuration independency on load and interference in and between the cells. Inparticular, eIMTA reconfiguration is performed using layer 1 signaling,namely by employing a downlink control information (DCI) of format 1C.Format 1C is used in the LTE for very compact transmission of PDSCHassignments, where the PDSCH transmission is constrained to QPSK such asfor paging messages and broadcast information messages among which theuplink/downlink configuration may be transmitted.

Thus, DCI format 1C may be advantageously used for reconfiguring theuplink/downlink configuration as well as the special subframeconfiguration for the purpose of short latency as described in the aboveembodiments and examples.

In order to ensure backward compatibility and maintain the systemdesign, a special RNTI may be used for short-latency reconfigurations.This means that DCI with the short-latency reconfiguration will be onlydetected by the UEs with the special RNTI, the special RNTI differingfrom the remaining RNTIs employed for UEs or groups of UEs.

Moreover, advantageously, the special subframe configuration and theuplink/downlink configuration are carried in a first field specifyingwhich subframes are special subframes and a second field specifying forthe special subframes which symbols belong to uplink and which symbolsbelong to downlink.

For example, the DCI carrying the short-latency reconfiguration may forthis purpose comprise the first field specifying which subframes areshort-TTI special subframes (i.e., special subframes supporting shortTTIs, i.e., TTIs shorter than TTI used for the uplink and downlinksubframes). The first field may have length of 6 or less bits per radioframe, depending on the number of configurations provided in the set ofselectable configurations (such as the tables in FIG. 5 or 12). Thefirst field should not need more than 10 bits when we assume thatsubframe pattern defined by the first field represents one subframe perbit, and the pattern repeats every 10 ms. An advantage of such a 10-bitfield is that it can be used to indicate not only whether a specialsubframe is configured as a short-TTI special subframe, but could evenindicate whether regular downlink or uplink subframes are configured asa short-TTI subframe. However when only subframes configurable for MBSFNplus subframes #1 and #6 are potential short-TTI special subframes, only7 subframes are such candidates and therefore a first field size of 7bits for a 10 ms pattern are necessary. In fact, when employing theembodiment that only subframes configurable as MBSFN plus subframe #6 ofa radio frame (i.e., only subframes #3, #4, #6, #7, #8, #9) areconfigurable as additional special subframes, and if only the additionalspecial subframes are available for short-TTI transmissions, then afirst field containing 6 bits would be sufficient to define a 10 mspattern that repeats every 10 ms, which is aligned with the MBSFNpattern repeating every 10 ms. An alternative additional specialsubframe pattern could be likewise defined for the case that the MBSFNconfiguration repeats every 40 ms, in which case a first field of length24 bits would be sufficient to represent each additional specialsubframe candidate in a 40 ms period. The size of the first field may befurther reduce to 5 bits in a 10 ms pattern (or 20 bits in a 40 mspattern) if only subframes configurable as MBSFN of a radio frame areconfigurable as short-TTI special subframes.

The DCI carrying the short-latency reconfiguration may further comprisethe second field specifying the special subframe configuration, i.e.,the number of symbols for the uplink portion and the number of symbolsfor downlink portion. The second field may have length of 6 or lessbits. 7 bits should be sufficient to provide sufficient flexibility (cfTables in FIGS. 6 and 8).

FIG. 13 illustrates flow diagrams of methods according to an embodiment.

A method 1300B may be performed at a terminal (user equipment). Themethod 1300B is designed for transmitting data in a frame with subframesof a wireless communication system, each subframe being either an uplinksubframe accommodating uplink signal, a downlink subframe accommodatingdownlink signal or a special subframe including a downlink signalportion as well as an uplink signal portion. The method includes a stepof receiving 1310 a control signal including a special subframeconfiguration specifying the length of the uplink and/or downlinkportion of the special subframe. As described above, the reception ofthe configuration may be performed semi-statically and/or dynamically.For instance, the configuration is initially received via cell broadcastover RRC system information. Later, the (re)configuration 1310 may beperformed dynamically by DCI, for instance on the PDCCH in LTE. However,the present disclosure is not limited to dynamical signaling. The(re)configuration may alternatively or in addition be conveyed via RRCprotocol (semi-statically). The configuration may apart from the specialsubframe configuration also include the uplink/downlink configuration asexemplified above. The UE upon receiving the configuration applies theconfiguration to its further transmissions and receptions.

In particular, the method 1300B further comprises a step of mapping 1320user data and/or control data including feedback information in atransmission time interval, TTI, onto one subframe. Moreover, the lengthof a second TTI for mapping onto the uplink portion of a specialsubframe is shorter than a first TTI for mapping onto an uplinksubframe, or a first number of TTIs mapped onto the uplink subframe islarger than a second number of TTIs for mapping onto the uplink portionof a special subframe. In other words, the received configurationdetermines the symbols which may be used for uplink and, according tothe TTI length to be applied, the user data and/or the control data tobe transmitted in the uplink, are mapped to the resource grid. Themapped data within a radio frame are then transmitted 1330 over thewireless interface channel 1300.

It is noted that the configuration received in step 1310 may also beapplied to the data reception at the terminal. In particular, the UE mayperform the step of receiving 1395 a radio frame in which downlink dataare conveyed including downlink user data and downlink control data (forinstance PDSCH and PDCCH in LTE). The data are demapped 1390 from thereceived frame according to the received configuration ofuplink/downlink subframes and/or special subframes and/or TTIlength/number.

Another method 1300A is provided for receiving data in a frame withsubframes of a wireless communication system, each subframe being eitheran uplink subframe accommodating uplink signal, a downlink subframeaccommodating downlink signal or a special subframe including a downlinksignal portion as well as an uplink signal portion. The method 1300A maybe performed at the base station (eNB in LTE) and includes a step oftransmitting 1370 a control signal including a special subframeconfiguration specifying the length of the uplink and/or downlinkportion of the special subframe. The configuration which is transmittedis selected 1360 beforehand by the base station, for instance based onconfiguration received from another network entity, or based on thetraffic in the cell or based on the services to be conveyed in the cellor based on the user profiles, or the like. Specifically, it isbeneficial to consider the shortest possible guard period that is ableto support the required time advance offset for uplink transmissions bya UE, as well as quality of service (QoS) requirements regarding latencyof a service.

The method 1300A further comprises a step of receiving 1340 data mappedon special subframes according to the special subframe configuration. Inother words, the base station receives uplink radio frame including thedata from the terminal mapped and transmitted as described above withreference to the method 1300B, steps 1310-1330.

After receiving the frame 1340, a step of demapping 1350 is performed todemap user data and/or control data including feedback information in atransmission time interval, TTI, from one subframe, wherein the lengthof a second TTI for mapping onto the uplink portion of a specialsubframe is shorter than a first TTI for mapping onto an uplinksubframe, or a first number of TTIs mapped onto the uplink subframe islarger than a second number of TTIs for mapping onto the uplink portionof a special subframe. It is noted that the step of demapping 1350applies the configuration selected 1360 by the base station, transmitted1370 to the UE and applied 1320 by the UE.

Moreover, the base station may employ the selected configuration also totransmission of data. In particular, the method may further include astep of mapping 1380 the data to be transmitted to the UE based on theselected configuration which has also been transmitted 1370 to the UE.After the mapping 1380, the frame with the mapped data is transmitted1385 to the UE.

In accordance with another embodiment, a computer program productcomprising a computer-readable medium having a computer-readable programcode embodied thereon is provided, the program code being adapted tocarry out the present disclosure.

Other exemplary embodiments relate to the implementation of the abovedescribed various embodiments using hardware and software. In thisconnection a user terminal (mobile terminal) and an eNodeB (basestation) are provided. The user terminal and base station are adapted toperform the methods described herein, including corresponding entitiesto participate appropriately in the methods, such as receiver,transmitter, processors.

It is further recognized that the various embodiments may be implementedor performed using computing devices (processors). A computing device orprocessor may, for example, be general purpose processors, digitalsignal processors (DSP), application specific integrated circuits(ASIC), field programmable gate arrays (FPGA) or other programmablelogic devices, etc. The various embodiments may also be performed orembodied by a combination of these devices.

Further, the various embodiments may also be implemented by means ofsoftware modules, which are executed by a processor or directly inhardware. Also a combination of software modules and a hardwareimplementation may be possible. The software modules may be stored onany kind of computer readable storage media, for example RAM, EPROM,EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc.

It should be further noted that the individual features of the differentembodiments may individually or in arbitrary combination be subjectmatter to another embodiment.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present disclosure asshown in the specific embodiments. The present embodiments are,therefore, to be considered in all respects to be illustrative and notrestrictive.

Summarizing, the present disclosure relates to receiving andtransmitting data in a frame with subframes of a wireless communicationsystem, each subframe being either an uplink subframe accommodatinguplink signal, a downlink subframe accommodating downlink signal or aspecial subframe including a downlink signal portion as well as anuplink signal portion. A control signal includes a special subframeconfiguration specifying the length of the uplink and/or downlinkportion of the special subframe. The mapping and demapping of user dataand/or control data including feedback information in a transmissiontime interval, TTI, onto or from one subframe is then performed, whereinthe length of a second TTI for mapping onto the uplink portion of aspecial subframe is shorter than a first TTI for mapping onto an uplinksubframe, or a first number of TTIs mapped onto the uplink subframe islarger than a second number of TTIs for mapping onto the uplink portionof a special subframe. The data are received or transmitted accordingly.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A communication apparatus comprising: a receiver, which, inoperation, receives a control signal indicating a special subframeconfiguration including a length of an uplink portion of a specialsubframe including a downlink portion and the uplink portion, a secondtransmission time interval (TTI) for the uplink portion of the specialsubframe being shorter than a first TTI for an uplink subframe; and atransmitter, which, in operation, transmits user data based on thecontrol signal, wherein the special subframe configuration takes a valueout of: a first value indicating the length of the uplink portion, whichis not sufficient to accommodate the user data in the second TTI, and asecond value indicating the length of the uplink portion, which issufficient to accommodate the user data in the second TTI.
 2. Thecommunication apparatus according to claim 1, comprising a mapper,which, in operation, maps a sounding reference signal on the uplinkportion when the special subframe configuration takes the first value,and maps the user data on the uplink portion when the special subframeconfiguration takes the second value.
 3. The communication apparatusaccording to claim 1, wherein the special subframe consists of aplurality of symbols, and the special subframe configuration indicatesthe number of the plurality of symbols for the downlink portion and/orfor the uplink portion, and the special subframe further comprises aguard period separating the downlink portion and the uplink portion. 4.The communication apparatus according to claim 1, wherein the specialsubframe configuration takes a value out of a set of values, which arediffer with respect to at least one of a length of the downlink portion,the length of the uplink portion, and the second TTI.
 5. Thecommunication apparatus according to claim 1, wherein the control signalincludes an uplink/downlink configuration indicating each subframe of aframe is the downlink subframe, the uplink subframe or the specialsubframe, and the uplink/downlink configuration includes a first set ofsubframes that are configurable for multicast or broadcast, and a secondset of subframes that are not configurable for multicast or broadcast.6. The communication apparatus according to claim 5, wherein the specialsubframe configuration differs for the first and the second sets ofsubframes of the uplink/downlink configuration.
 7. The communicationapparatus according to claim 5, wherein the first set of subframes arefrom among those subframes that are configurable as multicast broadcastsingle-frequency network (MBSFN) subframes, or the second set ofsubframes are subframes with number 1 and/or
 6. 8. The communicationapparatus according to claim 1, wherein the second TTI differs from aTTI of the downlink portion of the special subframe.
 9. Thecommunication apparatus according to claim 1, wherein the control signalis transmitted as layer 1/layer 2 signaling.
 10. The communicationapparatus according to claim 1, wherein the uplink portion of thespecial subframe is comprised of a data portion onto which the user datais mapped and a portion onto which a sounding reference signal and/or arandom access channel preamble is mapped.
 11. A communication methodcomprising: receiving a control signal indicating a special subframeconfiguration including a length of an uplink portion of a specialsubframe including a downlink portion and the uplink portion, a secondtransmission time interval (TTI) for the uplink portion of the specialsubframe being shorter than a first TTI for an uplink subframe; andtransmitting user data based on the control signal, wherein the specialsubframe configuration takes a value out of: a first value indicatingthe length of the uplink portion, which is not sufficient to accommodatethe user data in the second TTI, and a second value indicating thelength of the uplink portion, which is sufficient to accommodate theuser data in the second TTI.